Nuclear Medicine — MCQs

A 30-year-old woman presented with complaints of bone pain and abdominal cramps. Her family says she has a history of abnormal behavior. The consultant doctor arrived at a provisional diagnosis based on the clinical features. Which of the following would be the best investigation to arrive at a definitive diagnosis?

Q157

Which of the following is the best imaging modality to diagnose neuroendocrine tumors (NETs)?

Q158

A patient who was diagnosed with prostate cancer is being investigated. The bone scan is reported as a super scan with increased uptake in the bones and reduced activity in the spleen. What is the reason for this super scan appearance?

Q159

What is the most useful investigation for localization of a parathyroid adenoma?

Q160

Which of the following best describes the image shown in patient with carcinoma prostate?

Nuclear Medicine Indian Medical PG Practice Questions and MCQs

Question 151: Which of the following imaging modalities is used to assess the distribution of functional renal tissue?

A. DMSA scan (Correct Answer)
B. DTPA scan
C. MAG3 scan
D. Iodocholesterol scan (I-123)

Explanation: **Explanation:** The correct answer is **A. DMSA scan**. **1. Why DMSA is correct:** Dimercaptosuccinic acid (DMSA) is a **static renal imaging** agent. It is labeled with Technetium-99m ($^{99m}Tc$) and is taken up by the **proximal convoluted tubules** of the renal cortex. Because it binds to the renal parenchyma and remains there for a significant period (low excretion rate), it is the gold standard for assessing the **distribution of functional renal tissue**, calculating differential renal function, and detecting cortical scarring (e.g., in chronic pyelonephritis) or ectopic kidneys. **2. Why other options are incorrect:** * **DTPA scan ($^{99m}Tc$-Diethylene Triamine Pentaacetic Acid):** This is a **dynamic** imaging agent cleared solely by **glomerular filtration**. It is used to estimate the Glomerular Filtration Rate (GFR) and evaluate obstructive uropathy. * **MAG3 scan ($^{99m}Tc$-Mercaptoacetyltriglycine):** This is also a **dynamic** agent, primarily cleared by **tubular secretion**. It is the preferred agent for assessing renal perfusion and drainage, especially in patients with impaired renal function. * **Iodocholesterol scan:** This is used for **adrenal cortex imaging** (e.g., to localize functional tumors in Cushing’s syndrome or Conn’s syndrome), not for renal parenchymal assessment. **Clinical Pearls for NEET-PG:** * **Best for Cortical Scarring/Pyelonephritis:** DMSA Scan. * **Best for GFR estimation:** DTPA Scan (Gates method). * **Best for Renal Function in Neonates/Renal Failure:** MAG3 (due to high extraction fraction). * **Diuretic Renography:** Done using DTPA or MAG3 with **Furosemide (Lasix)** to differentiate between mechanical obstruction and functional stasis.

Question 152: Which of the following imaging modalities is used to assess the distribution of functional renal tissue?

A. DMSA scan (Correct Answer)
B. DTPA scan
C. MAG3 scan
D. Iodocholesterol scan (I-123)

Explanation: **Explanation:** The correct answer is **A. DMSA scan**. **1. Why DMSA is correct:** Dimercaptosuccinic acid (DMSA) is a **static renal imaging** agent. It is labeled with Technetium-99m ($^{99m}Tc$) and is taken up by the **proximal convoluted tubules** of the renal cortex. Because it binds to the renal parenchyma and remains there for a significant period (low excretion rate), it is the gold standard for assessing the **distribution of functional renal tissue**, detecting cortical scarring (e.g., in chronic pyelonephritis), and identifying ectopic kidneys or horseshoe kidneys. **2. Why other options are incorrect:** * **DTPA scan ($^{99m}Tc$-Diethylene Triamine Penta-acetic Acid):** This is a **dynamic** imaging agent filtered solely by the glomerulus. It is primarily used to measure the **Glomerular Filtration Rate (GFR)** and evaluate obstructive uropathy. * **MAG3 scan ($^{99m}Tc$-Mercaptoacetyltriglycine):** This is also a **dynamic** agent, primarily secreted by the renal tubules. It is the preferred agent for assessing **renal perfusion and drainage** (renography), especially in patients with impaired renal function. * **Iodocholesterol scan:** This is used for **adrenal cortex imaging** (e.g., to localize adenomas in Cushing’s or Conn’s syndrome), not for renal parenchymal assessment. **Clinical Pearls for NEET-PG:** * **DMSA = Static/Structural** (Think "S" for Scars and Structure). * **DTPA/MAG3 = Dynamic/Functional** (Think "D" for Drainage and GFR). * **Best initial test for Vesicoureteral Reflux (VUR) complications:** DMSA scan (to look for cortical scarring). * **Agent of choice in Neonates/Renal Failure:** MAG3 is preferred over DTPA due to better extraction efficiency.

Question 153: Which one of the following devices converts radioactive emissions to light for detection?

A. Geiger counter
B. Photographic film
C. Scintillation counter (Correct Answer)
D. Radiotracer

Explanation: **Explanation:** The correct answer is **C. Scintillation counter**. **Why it is correct:** The fundamental principle of a scintillation counter is **scintillation**—the property of certain materials (like Sodium Iodide crystals doped with Thallium) to emit a flash of light (photons) when struck by ionizing radiation (gamma rays). This light is then captured by a **Photomultiplier Tube (PMT)**, which converts the light into an electrical signal. In nuclear medicine, this is the core technology used in Gamma cameras and PET scans to detect radiopharmaceuticals within the body. **Why other options are incorrect:** * **A. Geiger counter:** This device uses **gas ionization**. Radiation ionizes gas molecules (usually Argon) inside a tube, creating an electrical pulse directly. It does not involve a light-conversion step. * **B. Photographic film:** While film can be darkened by radiation (autoradiography), it is a chemical process involving the reduction of silver halide crystals, not a real-time conversion to light for electronic detection. * **D. Radiotracer:** This is the **source** of the radiation (e.g., Technetium-99m), not the detection device itself. **High-Yield Clinical Pearls for NEET-PG:** * **Crystal of choice:** The most common scintillator used in Gamma cameras is **Thallium-activated Sodium Iodide [NaI(Tl)]**. * **PET Scans:** Use different scintillators like **Bismuth Germanate (BGO)** or Lutetium Oxyorthosilicate (LSO) because they are denser and better at stopping high-energy 511 keV photons. * **Photomultiplier Tube (PMT):** Its role is to convert light to electrons (via the photoelectric effect) and then amplify that signal a million-fold.

Question 154: Radioisotope used in PET-CT scan?

A. Iodine
B. Radium
C. Cesium-131
D. 18F-FDG (Correct Answer)

Explanation: ***18F-FDG*** - It is a **glucose analogue** labeled with the positron-emitting isotope **Fluorine-18**, making it the ideal tracer for measuring metabolic activity in tissues. - It is widely used in PET-CT because highly metabolic cells (like cancer cells and active neurons) accumulate it, allowing visualization of **hypermetabolic activity**. *Iodine* - Refers typically to **Iodine-131** or **Iodine-123**, which are primarily used in **thyroid imaging** and therapy. - These isotopes are **gamma emitters** detected by SPECT, not positron emitters required for PET. *Radium* - **Radium-223** (Radium chloride) is an **alpha emitter** used therapeutically for **metastatic prostate cancer** affecting the bone. - It is not a positron emitter and is not designed for diagnostic functional imaging scans like PET. *Cesium-131* - **Cesium-131** is a low-energy **gamma emitter** primarily used in **brachytherapy seeds** for localized radiation treatment. - It does not undergo positron decay and is therefore unsuitable for generating the specific annihilation photons required for PET scanning.

Question 155: Ga-68 PSMA PET scan is used to diagnose which of the following conditions?

A. Lung cancer
B. Prostate cancer (Correct Answer)
C. Liver cancer
D. Colon cancer

Explanation: ***Prostate cancer***- **Ga-68 PSMA PET** scan targets **Prostate-Specific Membrane Antigen** (**PSMA**), a protein highly overexpressed on the surface of prostate cancer cells.- This scan is crucial for staging, restaging (e.g., in case of **biochemical recurrence** with rising **PSA**), and detecting metastatic foci of prostate carcinoma.*Lung cancer*- Diagnosis and staging of lung cancer primarily use **F-18 FDG PET/CT**, which identifies tumors based on high glucose uptake (the **Warburg effect**).- Lung malignancies do not typically overexpress **PSMA** to a clinically significant degree for diagnostic imaging.*Colon cancer*- Colon cancer (colorectal carcinoma) staging relies primarily on **CT** scans; **F-18 FDG PET** is used mostly for high-risk, recurrent, or metastatic disease.- **PSMA** expression is not a reliable or standard biomarker for routine clinical imaging of colon cancer.*Liver cancer*- Standard imaging for liver cancer (**Hepatocellular carcinoma**) involves dynamic contrast-enhanced **CT** or **MRI**.- While some advanced PSPCs (Prostate-Specific PET probes) might show incidental uptake, **PSMA** is not the target for diagnosing or staging primary liver malignancies.

Question 156: A 30-year-old woman presented with complaints of bone pain and abdominal cramps. Her family says she has a history of abnormal behavior. The consultant doctor arrived at a provisional diagnosis based on the clinical features. Which of the following would be the best investigation to arrive at a definitive diagnosis?

A. MRI
B. Ultrasonogram
C. Sestamibi scan (Correct Answer)
D. CT scan

Explanation: ***Sestamibi scan*** - The clinical features (bone pain, abdominal cramps, abnormal behavior being "bones, groans, and psychic moans") strongly suggest **primary hyperparathyroidism** due to hypercalcemia, which requires definitive localization of the culprit adenoma. - The **Technetium-99m Sestamibi scan** is the best definitive investigation because it is a functional imaging study that specifically identifies hyperactive parathyroid tissue, showing increased, persistent uptake relative to the thyroid gland. *MRI* - MRI is primarily a **structural imaging** modality and is usually reserved for cases where initial localization studies (like Sestamibi and Ultrasound) are equivocal or to assess for **ectopic parathyroid tissue** located deep in the neck or mediastinum. - It lacks the high **functional specificity** of the Sestamibi scan required to definitively confirm that the identified mass is the hyperfunctioning parathyroid adenoma. *Ultrasonogram* - Ultrasound is often the **initial screening tool** for identifying parathyroid adenomas in the neck, being easily accessible and inexpensive, but it is **operator-dependent**. - It is not considered the single best definitive test because it often fails to localize small, posterior, or **ectopic adenomas** and provides only structural, not functional, information about the gland. *CT scan* - CT scans provide excellent **anatomical detail** and are helpful in complex cases or for locating mediastinal/ectopic glands, especially when planning highly focused surgery. - Like MRI, CT is a structural study that identifies masses but does not definitively prove the **hyperfunctionality** specific to parathyroid adenomas, making Sestamibi superior for definitive diagnosis.

Question 157: Which of the following is the best imaging modality to diagnose neuroendocrine tumors (NETs)?

A. MRI
B. PET (Correct Answer)
C. CT
D. USG

Explanation: ***PET***- **PET** imaging, particularly using tracers like **Gallium-68 DOTATATE** or **DOTATOC**, is the best modality because it targets the **somatostatin receptors (SSTr)** highly expressed on most well-differentiated neuroendocrine tumors (NETs).- This molecular imaging technique offers the highest **sensitivity and specificity** for identifying the primary tumor, effectively staging the disease, detecting occult metastases, and assessing therapeutic response.*USG*- **Ultrasound (USG)** is often limited to screening the abdominal organs (like the liver or pancreas) but lacks the anatomical comprehensiveness and sensitivity required for definitive staging of systemic NET disease.- Its performance is highly **operator-dependent**, and it is generally poor for evaluating deeply located tumors or detecting **pulmonary** or **osseous** involvement.*CT*- **CT scans** provide excellent anatomical information, are essential for tumor size measurement (using **RECIST criteria**), and are often used as the anatomical backbone to complement functional imaging like PET/CT.- However, CT relies on structural changes (size and density) and is significantly **less sensitive** than somatostatin receptor PET for finding small primary tumors or widespread, metabolically active metastases.*MRI*- **MRI** offers superior soft tissue contrast compared to CT, making it highly valuable, especially for evaluating complex areas like the **liver parenchyma** for metastatic disease or specific NETs (e.g., pancreatic NETs).- Like CT, MRI is a structural modality and fails to provide the **functional information** that PET offers regarding the presence and density of **somatostatin receptors**, limiting its use for overall tumor burden assessment and staging compared to PET.

Question 158: A patient who was diagnosed with prostate cancer is being investigated. The bone scan is reported as a super scan with increased uptake in the bones and reduced activity in the spleen. What is the reason for this super scan appearance?

A. Increased uptake due to diffuse metastasis (Correct Answer)
B. Increased uptake by carcinoma prostate
C. Decreased uptake by adrenal glands and kidney
D. Increased uptake by the bone

Explanation: ***Increased uptake due to diffuse metastasis***- The **super scan** appearance is pathognomonic for **widespread skeletal metastasis**, particularly common in advanced prostate cancer, where nearly all the tracer is utilized by diffuse bony lesions.- The reduced or absent visualization of soft tissues (like the **spleen**, **kidneys**, and **bladder**) results from the extremely high proportion of the radiotracer being extracted by the vast surface area of the metastatic bone lesions.*Increased uptake by carcinoma prostate*- Bone scans (using Tc-99m MDP) primarily reflect **osteoblastic activity** in bone, not the direct uptake by the primary non-osseous tumor tissue in the prostate.- While uptake might occasionally be seen in the primary tumor due to adjacent bony involvement or calcification, this is not the cause of the diffuse **super scan** pattern across the entire skeleton.*Increased uptake by the bone*- While the super scan is characterized by increased uptake in the bone, this statement fails to detail the underlying pathological *reason*, which is the widespread **diffuse skeletal metastasis**.- Normal physiological uptake by bone would not lead to the non-visualization of the **kidneys** and **spleen**, which is a crucial defining feature of the super scan.*Decreased uptake by adrenal glands and kidney*- The non-visualization (or decreased uptake) in soft tissue organs, including the **kidneys**, is a *consequence* of the super scan pattern, not the underlying cause of the appearance.- The primary mechanism is the massive tracer uptake in the skeleton due to **diffuse pathological activity**, leaving insufficient free tracer for normal soft tissue background and excretion.

Question 159: What is the most useful investigation for localization of a parathyroid adenoma?

A. Sestamibi scan (Correct Answer)
B. USG
C. FDG PET
D. SPECT

Explanation: ***Sestamibi scan*** - **Sestamibi scan (Tc-99m MIBI)** is the **gold standard** for preoperative localization of parathyroid adenomas, with a sensitivity of 80-95% when combined with SPECT. - The radiotracer is taken up by both thyroid and parathyroid tissue, but is **retained longer in the hyperfunctioning parathyroid adenoma**, allowing for differential washout imaging. - Can be enhanced with **SPECT/CT** for better anatomical localization, especially for ectopic glands. *USG* - **Ultrasound (USG)** is a useful anatomical localization tool, particularly for glands in typical locations, but its sensitivity (70-80%) is operator-dependent and limited by gland size/location. - Often used as a **complementary first-line investigation** alongside Sestamibi, especially for guiding needle aspiration or confirming location. - Less sensitive for ectopic or small adenomas compared to Sestamibi. *FDG PET* - **Fluorodeoxyglucose (FDG) PET** is generally not the primary investigation for typical parathyroid adenomas as they do not show intense FDG avidity. - Its use is reserved primarily for **parathyroid carcinoma** localization or in cases where other modalities have failed. - **C-11 Methionine PET** or **F-18 Choline PET** are specialized functional scans with better utility for adenomas than FDG PET, but are less commonly available than Sestamibi. *SPECT* - **SPECT (Single-Photon Emission Computed Tomography)** is an imaging technique that **enhances Sestamibi scan** anatomical resolution (Sestamibi-SPECT or SPECT/CT), especially for small or ectopic adenomas. - SPECT alone without a radiotracer like Sestamibi is not useful; it is the **combination of Sestamibi tracer with SPECT imaging** that provides superior localization. - The option likely refers to this combined modality, but Sestamibi scan (with or without SPECT) remains the most useful overall investigation.

Question 160: Which of the following best describes the image shown in patient with carcinoma prostate?

A. A = Osteosclerotic secondaries in X-ray KUB, B= Skeletal metastasis in bone scan (Correct Answer)
B. A = Osteolytic secondaries in X-ray KUB, B= Skeletal metastasis in Bone scan
C. A = Osteonecrotic secondaries in X-ray KUB, B = normal study in bone scan
D. A = over-penetrated X-ray KUB, B= skeletal metastasis in bone scan

Explanation: ***A = Osteosclerotic secondaries in X-ray KUB, B= Skeletal metastasis in bone scan*** - The **X-ray KUB (A)** shows multiple areas of increased density (whiteness) in the lumbar vertebrae and pelvic bones, consistent with **osteosclerotic (bone-forming) metastases**, which are characteristic of prostate cancer. - The **bone scan (B)** demonstrates multiple areas of intense tracer uptake throughout the axial and appendicular skeleton, indicating widespread **skeletal metastases**. This pattern of uptake is typical for metastatic prostate cancer, as it is an osteoblastic tumor. *A = Osteolytic secondaries in X-ray KUB, B= Skeletal metastasis in Bone scan* - The X-ray image (A) clearly shows areas of **increased bone density (sclerosis)**, not bone destruction or lucency associated with **osteolytic lesions**. - While the bone scan (B) does show skeletal metastasis, the description of the X-ray as osteolytic is incorrect for prostate cancer, which typically causes osteosclerotic lesions. *A = Osteonecrotic secondaries in X-ray KUB, B = normal study in bone scan* - **Osteonecrosis** refers to bone death due to lack of blood supply and would appear differently on X-ray, usually as areas of increased density mixed with lucency, often with a different distribution; the current image shows widespread blastic changes. - The bone scan (B) is distinctly **abnormal**, showing multiple hot spots consistent with metastatic disease, and is therefore not a normal study. *A = over-penetrated X-ray KUB, B= skeletal metastasis is bone scan* - An **over-penetrated X-ray** would appear very dark with poor contrast between bone and soft tissue, which is not the case in image A. Image A shows detailed bone structures with areas of increased density. - While image B correctly identifies skeletal metastasis, the description of image A as an over-penetrated X-ray is inaccurate given the clear radiographic findings of increased bone density.

Practice by Chapter

Physics of Nuclear Medicine

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Radiopharmaceuticals

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Radiation Detection in Nuclear Medicine

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Thyroid Scintigraphy

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Bone Scintigraphy

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Renal Nuclear Medicine

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Cardiac Nuclear Medicine

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Pulmonary Nuclear Medicine

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Neurological Nuclear Medicine

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PET/CT Principles and Applications

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Radionuclide Therapy

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Radiation Safety in Nuclear Medicine

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